Fiber placement is a process where a band, made up of several strips of composite fiber "tows", is automatically placed onto the surface of a mandrel or a workpiece that is molded into the shape of the composite part to be formed. The band is applied to the surface being fabricated and is compacted by a compliant pressure roller "head" under program control to remove the bulk. Critical to the success of the fiber placement process is the path of the tows from the material supply "creel" to the nip point "collation surface." If the composite tows are allowed to become twisted while traveling from the creel to the head, tow twist defects will result, which dramatically reduces the quality of the formed composite parts. Thus, in an effort to prevent tow twists and other composite forming defects from occurring, redirect devices have been implemented that help to keep individual incoming composite tows straight and separated from one other.
However, when fiber placement techniques are utilized to produce parts having highly contoured surfaces, as is required for complex contoured parts and fiber steering, the redirect device must ideally allow the tows to move freely towards the creel (backwards) as well as towards the collation surface (forwards), accommodate for the relative motion between the head and the creel of a six axes of motion fiber placement assembly, and contain the tows for efficient machine operation. Additionally, during the fiber placement forming process the fiber placement head initially makes contact with the collation surface and causes the head to retract slightly, which moves the fiber material backwards towards the creel due to a shortening of the distance between the fiber placement head and the creel. While current devices accommodate many machine motions, they do not allow the tows to move freely in both directions (towards the nip point and towards the creel) nor do they contain the tows well enough to allow for efficient machine operation. Thus, when the necessary backward motion is attempted with existing redirects, twisting of the composite tows frequently occurs, resulting in large amounts of tow twist defects in the formed composite parts. Such occurrences dramatically reduce part quality and machine productivity.
Previous fiber placement redirects, such as those issued to Vaniglia (U.S. Pat. Nos. 4,872,619 and 4,877,193), Steidle et al. (U.S. Pat. No. 5,239,193), and Grimshaw et el. (U.S. Pat. No. 5,273,614), all utilize rollers that can only compensate for one degree of freedom at a time. As a result, three sets of rollers would be needed to compensate for the three axes (yaw, pitch, and roll) that are utilized by a fiber placement head that moves subject to six axes of machine motion. Fiber placement heads that move in this manner are required for the production of some modern aerospace structures that have highly contoured surface configurations. Further, the previously mentioned fiber placement redirect devices are all designed to be utilized in conjunction with a gantry style placement head machine which is fundamentally different from the type of fiber placement assembly utilized with the present invention. In addition, none of the previously mentioned fiber placement redirect devices sufficiently accomodate bi-directional tow movement which is critical in producing highly contoured parts without tow twist defects. Thus, there is a continuing need for a fiber placement redirect that allows for bi-directional tow movement, can accommodate six axes of machine motion, and can contain the tows for efficient machine operation.